The main hypothesis of the three projects included in this application is that many of the important in vivo effects of nicotine in the CNS are mediated mainly by the desensitization of neuronal nicotinic acetylcholine receptors (nAChRs), specifically a4p2 nAChRs, which are the major nAChR in the CNS and the one most clearly affected (up-regulated) by chronic administration of nicotine in rats and mice and by smoking in humans. Our hypothesis has deep roots in both cellular studies and studies ofthe in vivo effects of nicotine in animals going back more than 20 years. We recently reported that a new nAChR ligand sazetidine-A (Saz-A) is a selective a4|32 nAChR desensitizer. Thus its major in vitro effect is to desensitize 04(32 nAChRs without affecting either a3p4 or a7 nAChRs. Of particular importance, Saz-A in vivo can substitute for nicotine in drug discrimination studies and, even more important, it decreases nicotine self-administration in rats. We therefore propose further in depth studies of the effects of Saz-A, including its effects during chronic administration, as well as the synthesis and development of additional new selective a4p2 desensitizing ligands. Our proposed research consists of three projects. In Project 1, we will use pharmacological methods to characterize new ligands at nAChRs in vitro, as we have done for Saz-A. These in vitro cellular studies will identify the best candidates for detailed in vivo studies outlined in Project 2. In Project 2, the effects of Saz-A and additional ligands identified in project 1 will be further evaluated for their effects on nicotine self-administration in the rat model. In Project 3, synthesis of new ligands based on Saz-A will be carried out to optimize the new ligands, with respect to their pharmacology and pharmacokinetic characteristics, which will allow selection of the dose range for the in vivo studies of project 2. In addition, project 3 will provide acute toxicity data for promising ligands and will synthesize the ligands in the quantities necessary for the detailed in vivo studies in project 2. A major goal of our proposed research is that it will lead to the development a new class of CNS therapeutics, selective a4p2 nAChR desensitizers, to aid smoking cessation.